The present invention relates broadly to a phase shifter apparatus, and in particular to a T-section digital phase shifter apparatus.
In modern high frequency radar and communication systems, the antenna pattern must be moved at very rapid rates and this is normally achieved in array antennas through the use of a matrix of small radiator elements whose radiation phases are systematically and electronically varied. The necessary phase gradients across the antenna are usually generated in discrete steps by a plurality of such electronic phase shifter elements.
A major handicap in the prior art phase shifter elements has been in the inability to exactly reproduce the diodes upon which the characteristics of the diode phase shifter elements are significantly dependent. However, this problem has been essentially solved by semiconductor manufacturers, so that attention has turned to the improvement of the phase shifter elements themselves. The design of the present phase shifter elements permits it beneficially to be physically smaller than the conventional elements of the loaded transmission line type.
In the military market, there is an increasing demand to design monolithic-digital phase shifters with very low insertion loss requirements. As the frequency increases, the insertion loss requirements become difficult to meet. Recent advances in the art have produced a 4-Bit monolithic digital phase shifter which uses conventional design approaches but only achieves about 5 dB insertion loss at 10 GHz which is excessively large for most military applications. Clearly, there is a need for new techniques in designing monolithic digital phase shifters with low insertion loss at high frequencies (X-Band and above). In the present invention, a T-section digital phase shifter suitable for extra high frequency applications with low loss and excellent phase tracking capability (i.e. wide bandwidth) is presented. The T-section digital phase shifter can easily be implemented as a monolithic circuit on many available substrates, such as, Si, GaAs, GaInAs, InP, etc.